Manufacture of electric cables



P. V. HUNTER MANUFACTURE OF ELECTRIC CABLES May 26, 192s.` 1,539,490

Filed Dec, 13, 1922 E vl/emot:

Patented May-26, 1925.

UNITED y STATESv 1,539,490 PATENT OFFICE.

PHILIP VASSAR HUNTER, OF LONDON, ENGLAND.

MANUFACTURE or ELECTRIC CABLES.

Application filed December 13, 1922. Serial No. 606,714.

To aZZ 'whom t mag/concern."

Be it. known that I, PHILIP VAssAR HUN- TER, a subject of the King ofEngland, and

. sulated say by pap-er wound round the conture that it is no longer suiiiciently liquidl ducting core, are impregnated or .immersed in a hot insulating composition.

" For Various reasons it is desirable that this insulating composition shall be of such a nature that it is ysolid or semi-solid when cold, but when heated to the requisite temperature it \must be suiiiciently liquid to penetrate the paper insulation. After the process of impregnation in the hot composition has proceeded for avsuflicient time the cooling process is allowed to commence and hitherto the cooling of the cable itself has necessarily started from the outside. In other words there is always during cooling a temperature gradient from the core or inner portion of the cable to the outer portion. Consequently as the cooling continues, a stage is reached when the insulating composition in or surrounding the outer portion of the cable is at such a temperato How or penetrate the paper. The core and inner layers of insulation are, however, still relatively hot and as they cool, the insulating composition around and in themy decreases iny volume and cannot be replenished, at anyvrate to the full extent, from outside owing to the viscosity of the comparatively cool composition. As a result the impregnation is not so effective as it might otherwise be.

According to the present invention this disadvantage is obviated by cooling the core of the cable atan appropriate stage in the impregnating process lso that the cooling of the composition takes place, at any rate partly, from inside. As compared with the usual practice there is preferably an actual reversal of the temperature gradient, the core being definitely cooler than the outside of the cable but in all cases the effect of the cooling of the core is at any rate to lessen or neutralise the gradient now always presenta Y Vusual in such cables.

In order that it may be possible thus to cool the core and inner portions of the cable it is preferred to provide the cable with a tube through which a cooling Inedium may be passed. This tube may conveniently be of copper and in close contact with the conductors forming the core.

F or instance stranded conductors may be laid up round a lcentral conducting tube which thus itself acts as part of the core. Again the whole core may in some instances form the tube or be constituted by it'. When the tube is surrounded by the stranded conductors forming the core, the cross sectional area of the bore of the tube may be say 20% of the total cross sectional area of the conductors.

In the accompanying drawings,

Figures l and 2 are respectively an elevation and a cross section of one construction of electric cab-le according to this invention, and

Figures 3 and 4 are similar views of an alternative construction of cable also according to this invention. n

Each of these constructions is given by wayof example only.

In both examples three-phase cables are shown but obviously the invention may be applied to other cables.

In Figures 1 and 2 the conducting core is formed partly by a tube A, preferably of copper, and partly by stranded conductors B laid up round the tube A in close contact with it. The insulation C surrounding each. conducting core is preferably of paper or some insulating material which, after being wound round the core in some wellknown way, is impregnated in the manner The outer insulation and covering E may be Vof any' known form andv do not in themselves form part of the present invention.

In the example shown. in Figures 3 and i the conducting core consists solely of the tube A.

After each of the cables formed by the core A B or A and the insulation C has ingprocess isto be commenced any convenient cooling medium is passed through the tube A or A. Such medium may if desired be an insulating liquid. This however is not essential for no passage of the cooling medium into the insulation of the cable is possible and it is convenient to use refrigerated brine.

It is to be understood that it is not essential for the carrying out of this invention thatl the Whole cooling of the cable 'shall proceed from the inside. In some impregnatmg processes the cooling of the 1n-L sulating composition is hastened by causing a cooling medium' to be circulated through tubes immersed in the composition and such a method may be used in conto secure by Letters Patent isz- A method of impregnatinr the insulation of an electric cable in which after the impregnation process has proceeded for a sufficient time the core or conductor is cooled by means of a cooling medium, such for example as refrigerated brine passed through the interior of the cable.

In testimony whereof I have signed my name to this specification.

PHILIP VASSAR HUNTER. 

